the instructions for taking a screenshot are not working for me on a MacBook Pro

Can you use the ScreenShot Application? Take screenshots or screen recordings on Mac - Apple Support

What happens when you press Shift + Command + 3 or Shift + Command + 4?

You don't see the screenshot on your desktop?

After you press the keystrokes ( and in the case of Shift + Command + 4, select the area you want to capture), do you not see a small thumbnail of the image appear briefly in the corner of you screen?

MtD